The present invention relates to a monopulse radar system designed to perform homing functions for a missile.
Airborne radar applications. utilizing monopulse techniques are widely used, particularly for military applications. Monopulse or simultaneous type radar systems are distinguished from sequential type systems by the derivation of the positional information from each reflected pulse rather than from a succession of reflected pulses. In one type of monopulse system, a pair of antennas are spaced apart in a plane so that the relative phase relationship of the reflected waves received by these antennas is utilized to provide the positional information for one coordinate.
Another known form of simultaneous, or monopulse, system is the so-called amplitude comparison system. This again utilizes a pair of antennas and receiver channels for each coordinate but has the antennas effectively located at a common point with their directive axes diverging from the common axis of the array. As is well-known to those skilled in the art, one coordinate of the target may be determined from a comparison of the relative amplitudes of the signals received by the antennas of each pair.
One problem encountered by all radar systems is that of detecting targets that are obscured by nearby clutter. In airborne radar systems which are used to provide homing for missiles, ground clutter presents a problem, as ground clutter can be greater than the radar cross section of the target and target echoes are embedded and lost in the ground clutter echoes.
Various schemes and devices are employed to overcome the problems presented by clutter. One such system is described in U.S. Pat. No. 3,392,387, which issued July 9, 1968, to George M. Kirkpatrick. In this patent, a system is described which utilizes monopulse technique to place a null in the elevation angle so as to reduce the ground clutter received by an airborne radar system. The monopulse null is caused to scan in elevation angle so as to maintain the null at the angle of arrival of the echo from clutter elements. As the transmitted range pulse sweeps outward along the ground and reflects from ground clutter, the null in the elevation plane scans through the elevation angles and the range display shows virtually no return. When a target is encountered displaced from the null direction no cancellation occurs and the range display shows the target.